The present invention relates generally to a method of manufacturing dental restorations and restorations produced therefrom and more specifically a method of using metal powders to manufacture dental restorations.
Conventional techniques used in the manufacture of dental restorations involve the casting of materials such as metals and ceramics and employ the xe2x80x9clost waxxe2x80x9d process. As known in the industry, the lost wax technique consists of a number of successive operations which begin with the dentist taking an impression of the patient""s teeth. The impression allows a model or die to be made of the teeth, which the dental technician then uses to build a wax pattern thereon of the article to be made. The wax is burned out and the metal, alloy or ceramic is cast into the void left by the wax. This process is time consuming and involves complex steps.
Alternative methods have been proposed including those involving the sintering of metals. In many of the methods, more than one heating step is required to obtain the metal core. In U.S. Pat. No. Re. 33,371, metal powder is applied to a model and heated. A second application of metal powder is performed and the model is heated again. In addition to the many required heating steps, the metallic mixture may run on the model before sintering, thus damaging the dimensional accuracy of the product and making it difficult to achieve consistent thickness.
In EP 523019, metal powder is applied onto a model and the model must then be plunged into a small paper cylinder, filled with a material, known as covering material. The material prevents running and deformation and is mechanically removed when sintering has been performed. Although the covering material filled in the cylinder is able to prevent the material from running, the inventors herein have found that the covering material used in the cylinder is too thick, takes longer to dry, requires high sintering temperatures and promotes tearing and cracking on the metal coping.
It is desirable that metal restorations be provided having no cracking and tearing problems. It is beneficial that the manufacturing steps be reduced to provide high strength dental restorations.
These and other objects and advantages are accomplished by the process wherein metal powder materials are used to form dental restorations. In one embodiment herein, metal powder is applied to a die or model of a tooth for which a restoration will be made. The metal powder may comprise one or more precious metals, non-precious metals and alloys thereof. Preferably, the metal powder is a high fusing metal and preferably, the metal powder comprises a non-oxidizing metal. The metal powder may comprise a multimodal particle size distribution to achieve high density during sintering. The multimodal particle powder comprises larger or coarse particle size powder in combination with a smaller or fine particle size powder. After the metal powder is applied to the model, it is covered with a covering material such as a refractory die material preferably in the form of a flowable paste. Optionally, after the flowable paste has been applied onto the metal powder, a second covering material may be sprinkled or dusted onto the paste. The model is then dried prior to firing. After drying, the model is sintered to provide a high strength metal restoration. The sintering range depends upon the metal or alloy being used. The sintering temperature is close to but below or in the low range of the melting temperature range of the layer of alloy powder, or if a metal powder is used, the sintering temperature will be close to, but below the melting point of the metal powder. After sintering, the outer shell can be broken off easily with one""s hand to expose the sintered coping. The coping is then easily removed from the die absent any adherence problems.
In an alternate embodiment of the process herein, after a high melting metal powder has been applied to the die, a mass or ball of lower melting metal or alloy or powder of metal or alloy is placed or disposed on the metal powder layer. The mass acts as a reservoir of material which will flow into the metal powder interstices formed from the first metal or alloy layer. The process continues as above, whereafter sintering, the outer shell can be broken off easily with one""s hand to expose the sintered coping. The coping is then easily removed from the die absent any adherence problems.
In yet another embodiment herein, after the metal powder layer is applied to the die, a ceramic or porcelain material is applied to the unsintered metal layer. The porcelain appears to act as a thermal barrier to help in holding the coping in place, prevent margin creeping and lifting. There is no need to apply a covering layer prior to sintering and there is no need to apply an opaque layer after the sintering process and prior to finishing the coping with porcelain to achieve the finally desired product.
In still another embodiment, a heat-absorbing material is applied to the die prior to application of the metal layer, and optionally, a heat-absorbing material is further applied onto the metal layer after it has been formed onto the die, and is also applied onto other components, such as a sprue or reservoir, that may be disposed on the metal layer. The heat-absorbing material increases the absorption of radiant heat to provide faster, more efficient, sintering kinetics.
The invention also includes various finishing processes including pressing ceramic onto the metal coping or applying fiber-reinforced composite materials or polymeric materials to the metal copings.
The processes and materials herein may be used to manufacture dental appliances including but not limited to orthodontic retainers, bridges, space maintainers, tooth replacement appliances, dentures, posts, crowns, posts, jackets, inlays, onlays, facings, veneers, facets, implants, abutments, splints, partial crowns, teeth, cylinders, pins, and connectors.